<!DOCTYPE html>
<html>
<head>
  <script src="https://cdn.rawgit.com/konvajs/konva/1.4.0/konva.min.js"></script>
  <meta charset="utf-8">
  <title>Konva Multi-touch Scale Shape Demo</title>
  <style>
    body {
      margin: 0;
      padding: 0;
      overflow: hidden;
      background-color: #F0F0F0;
    }
  </style>
</head>
<body>
  <div id="container"></div>
  <script>
    var width = window.innerWidth;
    var height = window.innerHeight;

    var lastDist = 0;
    var startScale = 1;
    var activeShape = null;

    function getDistance(p1, p2) {
        return Math.sqrt(Math.pow((p2.x - p1.x), 2) + Math.pow((p2.y - p1.y), 2));
    }

    var stage = new Konva.Stage({
        container: 'container',
        width: width,
        height: height,
        draggable: true,
        x: width / 2,
        y: height / 2,
        offset: {
            x : width / 2,
            y : height / 2
        }
    });

    var layer = new Konva.Layer();

    var triangle = new Konva.RegularPolygon({
        x: 190,
        y: stage.getHeight() / 2,
        sides: 3,
        radius: 80,
        fill: 'green',
        stroke: 'black',
        strokeWidth: 4,
        draggable: true,
        name: 'triangle'
    });

    var circle = new Konva.Circle({
        x: 380,
        y: stage.getHeight() / 2,
        radius: 70,
        fill: 'red',
        stroke: 'black',
        strokeWidth: 4,
        draggable: true,
        name: 'circle'
    });

    stage.on('tap', function(evt) {
        // set active shape
        var shape = evt.target;
        activeShape = activeShape && activeShape.getName() === shape.getName() ? null : shape;

        // sync scene graph
        triangle.setAttrs({
            fill: activeShape && activeShape.getName() === triangle.getName() ? '#78E7FF' : 'green',
            stroke: activeShape && activeShape.getName() === triangle.getName() ? 'blue' : 'black'
        });

        circle.setAttrs({
            fill: activeShape && activeShape.getName() === circle.getName() ? '#78E7FF' : 'red',
            stroke: activeShape && activeShape.getName() === circle.getName() ? 'blue' : 'black'
        });

        layer.draw();

    });

    stage.getContent().addEventListener('touchmove', function(evt) {
        var touch1 = evt.touches[0];
        var touch2 = evt.touches[1];

        if(touch1 && touch2 && activeShape) {
            var dist = getDistance({
                x: touch1.clientX,
                y: touch1.clientY
            }, {
                x: touch2.clientX,
                y: touch2.clientY
            });

            if(!lastDist) {
                lastDist = dist;
            }

            var scale = activeShape.scaleX() * dist / lastDist;

            activeShape.scaleX(scale);
            activeShape.scaleY(scale);
            layer.draw();
            lastDist = dist;
        }
    }, false);

    stage.getContent().addEventListener('touchend', function() {
        lastDist = 0;
    }, false);

    layer.add(triangle);
    layer.add(circle);
    stage.add(layer);
  </script>

</body>
</html>